1. Technical Field
The present invention relates to an electrophoretic display device, a method of driving an electrophoretic device, and an electronic apparatus.
2. Related Art
In order to display an image with an electrophoretic display device, an image signal is once stored in a memory circuit through a switching element. The image signal stored in the memory circuit is directly input to a pixel electrode, and, when the pixel electrode is applied with an electric potential, a difference in electric potential is generated between opposite electrodes. Thus, an electrophoretic element is driven to be able to display an image (which is, for example, described in JP-A-2003-84314). In addition, JP-A-2003-84314 describes a configuration that includes an SRAM (Static Random Access Memory) as a memory circuit (a configuration in which a latch that holds a piece of information in the form of electric potential is provided in a pixel) and also describes a configuration that includes a DRAM (Dynamic Random Access Memory) as a memory circuit (a configuration in which an electric potential is held by a capacitor).
In order to display an image with the electrophoretic display device, a sufficient difference in electric potential has to be applied between the electrodes that hold the electrophoretic element therebetween, so that the power supply voltage of the memory circuit needs to be 10 V or above. At this time, when the adjacent pixels are displaying different colors, the pixel electrodes of the adjacent pixels are input with different electric potentials. Therefore, because a large difference in electric potential occurs between the adjacent pixel electrodes, a leakage current flows between adjacent first electrodes through an adhesive, or the like, that fixes the electrophoretic elements to the substrate. Although a leakage current per pixel is small, a leakage current over the entire display portion of the electrophoretic display device is large. This has caused an increase in power consumption. Note that the occurrence of the leakage current will be specifically described later in an embodiment with reference to FIG. 10.
Moreover, the occurrence of a leakage current means that there is a possibility that an electrochemical reaction may occur in the pixel electrodes. That is, there has been a possibility that the reliability of the pixel electrodes is deteriorated because of generation of ion migration or corrosion. Then, for example, when a material, such as gold or platinum, that is chemically stable and anticorrosive, is used for the pixel electrode, the reliability may be improved; however, manufacturing costs will increase.
Furthermore, in an active matrix electrophoretic display device, when the screen is switched from an image (original image) that has been already displayed to an image (new image) that will be displayed next, a pre-display operation is executed in order to prevent after-image. For example, an operation by which white display is performed over the entire display portion (all white display), an operation by which black display is performed over the entire display portion (all black display), an operation by which all white display and all black display are alternately executed, an operation by which the inverted image of an original image or a new image is displayed for a short time, or the like, is executed. Then, after such a pre-display operation has been performed, a new image will be displayed.
An image switching sequence that includes the above pre-display operation is absolutely necessary to achieve a high-quality (high contrast, after-image free) under circumstances in which the electrophoretic display device is used. However, in the above image switching sequence, it is necessary to transfer data of all white, all black or an inverted image to a pixel every time an image is switched and, therefore, it has caused an increase in power consumption of the electrophoretic display device.